The removal of chemical contaminants from wastewater and ground water has become an important problem in restoring ecological balance to polluted areas. It is known that some algal species are capable of absorbing heavy metals into their cell walls, thus reducing their toxic effects on the environment. Algae can also take up nutrients and micronutrients that may be present in overabundance, such as potassium, nitrogen, iron, aluminum, and calcium, and can thus be utilized to provide a remediating ecosystem. A system used to effect this uptake is known as periphyton or algal turf. A further advantage to this technique is that the enriched algae can be harvested and used as fish or animal feed, which serves to return the nutrients to the food chain.
Periphyton filters (PF) or algal turf have the potential for use in a variety of applications. For example, the turf can be used to replace biological or bacteriological filters in aquaria. As mentioned, algal turf can be used to remove nutrients and other contaminants from polluted waters. In addition, by harvesting the algal mass, various processes can be used to produce a biomass energy source such as methane or ethanol, fertilizer, a human or animal food additive or supplement, cosmetics, or pharmaceuticals.
Studies in algal turf production are known in the art. For more than 20 years, tropical reefs have been acknowledged to be among the most productive of natural systems. For example, in Lewis, "Processes of Organic Production on Coral Reefs," pp. 305-347, 52 Biol. Rev. (1977), coral reefs are cited as being among the highest producers in primary production values for pelagic, benthic, and terrestrial ecosystems.
Notwithstanding the values demonstrated in some earlier literature, recent efforts have demonstrated that those estimates of reef primary productivity were conservative. The mean reported value, 10.3 G/m.sup.2 /day, should be contrasted to values ranging from 19.2 to 32.7 G/m.sup.2 /day in a 1980 study on St. Croix reefs. Recent studies have demonstrated that algal turfs in conjunction with wave surges have been identified as the primary source of most reef productivity. The latest large-scale pilot plants in fresh water agricultural irrigation waters having algal turf or periphyton scrubbers with variable wave energies have repeatedly demonstrated productions averaging 35 g/m.sup.2 /d, with peaks well over 40 g/m.sup.2 /d.
It is known that the removal or reduction of wave surge motion can reduce primary productivity, and that the subtle manipulation of light in various patterns across the growing surface can fine tune the performance of periphyton filters or algal turf. This permits a desired speciation of algal turf to dominate, and thus specific forms of a particular pollutant can be more effectively removed. In some areas such as reef systems, a typical diurnal oxygen concentration cycle in a reef microcosm can be greatly affected by wave surge action. Fresh water systems are less affected.
Algal turf techniques have been disclosed in Adey's U.S. Pat. No. 4,333,263, "Algal Turf Scrubber," and the present inventor's U.S. Pat. No. 5,131,820, "Low Pressure, Low Head Buoyant Piston Pump for Water Purification." Adey teaches that a surge is necessary in algal turf scrubbers.
Additionally, a body of literature deals with algal techniques for waste recycling, oceanic farming, and the like. Contemporary research can be grouped in two distinct categories: that utilizing macroalgae and that using planktonic algae. The first group is discussed in Ryther et al., "Physical Models of Integrated Waste-Recycling Marine Polyculture Systems," Aquaculture 5, 163-77 (1975); California Institute of Technology, Graduate School Project, "Evaluating Oceanic Farming of Seaweeds As Sources of Organics and Energy," U.S. Department of Energy, Division of Solar Technology, Contract E (04-3)-1275; and Washington State Department of Natural Resources, "Aquaculture of Seaweeds on Artificial Substrates," U.S. Department of Commerce, Contract R/A-12. The case of planktonic algae is discussed in Goldman et al., "Relative Growth of Different Species of Marine Algae in Wastewater-Seawater Mixtures," Marine Biology, 28, 17-25(1974); Karolinska Institute, "Investigation of an Integrated Aquatic System for Storing Solar Energy in Organic Material," Namnden for Energiproduktionforskning, No. 53 3065 062; and State of Hawaii Natural Energy Institute, "Energy from Algae of Bioconversion and Solid Waste," Hawaii State Government.
In neither case has research to date utilized wave surge motion to enhance the exchange of metabolites between algal cells in the water medium. Also these known research techniques have not recognized the criticality of macroalgae size, vis-a-vis the shading of one cell by another. Accordingly, such techniques are not suitable for optimum biomass production, and the propensity of removing nutrients and other contaminants from polluted waters is severely limited.
Harvesting has been accomplished in prior art systems by simply scraping the algae off the surface, but this often incompletely removed portions of the algae and allowed these fragments and particles to be discharged into the water system. Thus the nutrients previously incorporated into plant mass or otherwise trapped were dislodged, decomposed, broken into small pieces, and flushed back into the waterway upon restarting the process design flow rates. It was to improve upon the procedure of growing, harvesting, and processing the algae and other trapped particulates and organisms on a large scale (acres or more) and to enable the construction of facilities in an economical fashion, across various geological surfaces with low bearing pressures, which optimize growing conditions for the algal or periphytic community and allow effective removal of bioassimilated or trapped pollutants after they have been taken up from the water, that the present invention was developed.